Hyponatremia Evaluation and Management Algorithm

Initial Assessment and Classification

Begin by confirming true hypotonic hyponatremia with serum osmolality measurement, then immediately assess symptom severity and volume status to guide urgent versus non-urgent management. 1

Step 1: Confirm True Hyponatremia

Measure serum osmolality to exclude pseudohyponatremia from hyperglycemia (add 1.6 mEq/L to sodium for each 100 mg/dL glucose >100 mg/dL) or hyperlipidemia 1
Calculate plasma osmolality: 2 × Na (mEq/L) + BUN (mg/dL)/2.8 + glucose (mg/dL)/18 (normal 275-295 mOsm/kg) 1
Obtain serum and urine osmolality, urine sodium, and uric acid 1

Step 2: Classify Severity

Mild: 130-134 mEq/L 2
Moderate: 125-129 mEq/L 2
Severe: <125 mEq/L 2

Step 3: Determine Symptom Severity (Dictates Urgency)

Severe symptoms (seizures, coma, confusion, altered consciousness, respiratory distress) constitute a medical emergency requiring immediate 3% hypertonic saline regardless of sodium level. 1, 3

Severe symptoms: Confusion, delirium, altered consciousness, seizures, coma, respiratory distress 3
Moderate symptoms: Nausea, vomiting, headache, muscle cramps, gait instability, lethargy, weakness 3
Mild/asymptomatic: Minimal or no symptoms 1

The rapidity of development determines symptom severity more than the absolute sodium level—acute hyponatremia (<48 hours) causes more severe symptoms than chronic hyponatremia at the same sodium concentration 3

Emergency Management: Severe Symptomatic Hyponatremia

For severe symptoms, administer 3% hypertonic saline immediately with a target correction of 6 mmol/L over 6 hours or until symptoms resolve, never exceeding 8 mmol/L in 24 hours. 1

Immediate Treatment Protocol

Give 3% hypertonic saline as 100 mL boluses over 10 minutes, repeating up to three times at 10-minute intervals until symptoms improve 1
Alternative: Calculate infusion rate = body weight (kg) × desired rate of increase (mmol/L/hour) 4
Target: Increase sodium by 6 mmol/L in first 6 hours 1
Absolute limit: Maximum 8 mmol/L increase in any 24-hour period 1

Monitoring During Acute Correction

Check serum sodium every 2 hours during initial correction 1
After severe symptoms resolve, check every 4 hours 1
ICU admission for close monitoring 1

Critical Safety Consideration

Never exceed 8 mmol/L correction in 24 hours—overcorrection causes osmotic demyelination syndrome (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) appearing 2-7 days after rapid correction. 1

Non-Emergency Management: Asymptomatic or Mildly Symptomatic Hyponatremia

Step 4: Assess Volume Status (Determines Treatment Strategy)

Physical examination has poor accuracy (sensitivity 41%, specificity 80%), so combine clinical findings with laboratory data 1

Hypovolemic Signs:

Orthostatic hypotension, tachycardia 1
Dry mucous membranes, decreased skin turgor 1
Flat neck veins 1
Urine sodium <30 mmol/L (extrarenal losses) or >20 mmol/L (renal losses) 1

Euvolemic Signs:

Normal blood pressure, no edema 1
Normal skin turgor, moist mucous membranes 1
Urine sodium >20-40 mmol/L with urine osmolality >300 mOsm/kg suggests SIADH 1
Serum uric acid <4 mg/dL has 73-100% positive predictive value for SIADH 1

Hypervolemic Signs:

Peripheral edema, ascites, jugular venous distention 1
Pulmonary congestion 1
Seen in heart failure, cirrhosis 1

Step 5: Measure Urine Osmolality and Sodium

Urine osmolality <100 mOsm/kg: Appropriate ADH suppression (primary polydipsia, beer potomania) 1
Urine osmolality >100 mOsm/kg: Impaired water excretion (SIADH, heart failure, cirrhosis) 1
Urine sodium <30 mmol/L: Hypovolemic hyponatremia (71-100% positive predictive value for saline responsiveness) 1
Urine sodium >20-40 mmol/L with high urine osmolality: SIADH 1

Treatment Based on Volume Status

Hypovolemic Hyponatremia

Discontinue diuretics and administer isotonic saline (0.9% NaCl) for volume repletion, with initial infusion rate 15-20 mL/kg/h, then 4-14 mL/kg/h based on response. 1

Correct underlying cause (gastrointestinal losses, diuretics, third-spacing) 1
Maximum correction: 8 mmol/L in 24 hours 1
High-risk patients (cirrhosis, alcoholism, malnutrition): limit to 4-6 mmol/L per day 1
Consider albumin infusion in cirrhotic patients 1

Euvolemic Hyponatremia (SIADH)

Fluid restriction to 1 L/day is the cornerstone of SIADH treatment; if no response, add oral sodium chloride 100 mEq three times daily. 1

First-line:

Fluid restriction to 1 L/day (or <800 mL/day for refractory cases) 1

Second-line (if fluid restriction fails):

Oral sodium chloride 100 mEq (approximately 6 grams) three times daily 1
Urea 15-30 grams daily (alternative to salt tablets) 1, 5

Third-line (resistant cases):

Vasopressin receptor antagonists (tolvaptan 15 mg once daily, titrate to 30-60 mg) 1
Loop diuretics, demeclocycline, or lithium (less commonly used) 1

Common SIADH causes to address:

Malignancies (especially small cell lung cancer) 1
CNS disorders (stroke, hemorrhage, infection) 1
Pulmonary diseases (pneumonia, tuberculosis) 1
Medications (SSRIs, carbamazepine, cyclophosphamide, NSAIDs, opioids) 1

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

Implement fluid restriction to 1-1.5 L/day for sodium <125 mmol/L, discontinue diuretics temporarily, and avoid hypertonic saline unless life-threatening symptoms are present. 1

Management strategy:

Fluid restriction to 1-1.5 L/day for sodium <125 mmol/L 1
Temporarily discontinue diuretics if sodium <125 mmol/L 1
Treat underlying condition (optimize heart failure therapy, manage cirrhosis) 1
Consider albumin infusion in cirrhotic patients (8 g per liter of ascites removed) 1
Avoid hypertonic saline unless life-threatening symptoms—it worsens edema and ascites 1

For cirrhosis specifically:

Sodium restriction (2-2.5 g/day) is more effective than fluid restriction for weight loss 1
Correction rate: 4-6 mmol/L per day maximum (never exceed 8 mmol/L in 24 hours) 1
Vasopressin antagonists (tolvaptan) may be considered for resistant cases but carry higher risk of GI bleeding (10% vs 2% placebo) 1

Special Populations and Considerations

Neurosurgical Patients: SIADH vs. Cerebral Salt Wasting (CSW)

Distinguishing CSW from SIADH is critical because they require opposite treatments—CSW needs volume and sodium replacement while SIADH requires fluid restriction. 1

Cerebral Salt Wasting (CSW):

Clinical features: True hypovolemia (orthostatic hypotension, tachycardia, dry mucous membranes, CVP <6 cm H₂O) 1
Laboratory: Urine sodium >20 mmol/L despite volume depletion 1
Treatment: Volume and sodium replacement with isotonic or hypertonic saline (50-100 mL/kg/day) 1
Severe symptoms: 3% hypertonic saline plus fludrocortisone 0.1-0.2 mg daily 1
Never use fluid restriction in CSW—it worsens outcomes 1

SIADH in neurosurgical patients:

Clinical features: Euvolemic (normal CVP, no orthostatic changes) 1
Laboratory: Urine sodium >20-40 mmol/L, urine osmolality >300 mOsm/kg 1
Treatment: Fluid restriction to 1 L/day 1

Subarachnoid hemorrhage patients at risk of vasospasm:

Never use fluid restriction—it increases cerebral ischemia risk 1
Consider fludrocortisone or hydrocortisone to prevent natriuresis 1

Cirrhotic Patients

Higher risk of osmotic demyelination syndrome—limit correction to 4-6 mmol/L per day 1
Hyponatremia increases risk of spontaneous bacterial peritonitis (OR 3.40), hepatorenal syndrome (OR 3.45), and hepatic encephalopathy (OR 2.36) 1
Even mild hyponatremia (130-135 mmol/L) should not be ignored 1

Patients with Advanced Liver Disease, Alcoholism, or Malnutrition

These high-risk patients require even more cautious correction at 4-6 mmol/L per day due to markedly increased risk of osmotic demyelination syndrome. 1

Management of Overcorrection

If sodium rises >8 mmol/L in 24 hours, immediately discontinue current fluids, switch to D5W (5% dextrose in water), and consider desmopressin to relower sodium. 1

Target: Bring total 24-hour correction back to ≤8 mmol/L from baseline 1
Monitor for osmotic demyelination syndrome signs (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) typically appearing 2-7 days after rapid correction 1

Common Pitfalls to Avoid

Ignoring mild hyponatremia (130-135 mmol/L) as clinically insignificant—it increases fall risk (21% vs 5%) and mortality (60-fold increase with sodium <130 mmol/L) 1, 3
Overly rapid correction exceeding 8 mmol/L in 24 hours causes osmotic demyelination syndrome 1
Using fluid restriction in CSW worsens outcomes and increases cerebral ischemia risk 1
Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms worsens edema and ascites 1
Inadequate monitoring during active correction leads to overcorrection 1
Failing to recognize and treat the underlying cause results in recurrent hyponatremia 1
Applying fluid restriction in subarachnoid hemorrhage patients at risk of vasospasm increases ischemic complications 1

Monitoring and Follow-up

During active correction:

Severe symptoms: Serum sodium every 2 hours 1
After symptom resolution: Every 4 hours 1
Asymptomatic/mild symptoms: Every 24-48 hours initially 1

Long-term:

Address underlying cause 1
Monitor for recurrence 1
Assess for complications of chronic hyponatremia (cognitive impairment, falls, fractures) 6
Correction of hyponatremia improves cognitive function and quality of life 3

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